Papermaking system including a flexible ceramic member having a pre-loaded tensile force applying means

ABSTRACT

A system for use in papermaking including at least two members one of which is movable relative to the other and in frictional engagement therewith wherein at least one of the members comprises an elongated flexible composite including a plurality of ceramic segments, each segment having at least two opposite surfaces that are flat and parallel. The segments are aligned in stacked relationship with their flat faces in abutting face-to-face relation and forced toward each other in the direction of their composite length with a force which is sufficient to maintain the segments in compression when subjected to conditions of thermal change and/or flexing of the member during use. The ceramic member is provided with a smooth elongated working surface which defines an area of contact between the members of the system. Systems including a papermaking foil or suction device in a papermaking process, or a doctor blade are disclosed. A method for making the ceramic member is disclosed.

This application is a continuation-in-part of Ser. Nos. 273,027 filedJuly 19, 1972; 273,307, filed July 19, 1972; and 377,893, filed 10,1973, all now abandoned. Further, this application is related to Ser.No. 377,894, filed July 10, 1973.Iadd., now U.S. Pat. No. 3,869,344..Iaddend.

This invention relates to papermaking systems including two members thatare movable relative to one another, and more particularly to awear-resistant, flexible member which is useful in applications wherethe member is to be subjected to conditions of thermal change and/orforces tending to bend the member along its length.

The physical properties and/or the chemical inertness of ceramicmaterials frequently suggest such materials for use in applicationswherein the material is to be subjected to potential physical and/orchemical degradation as by frictional forces, corrosion, or othererosive forces. Not infrequently, ceramic elements or members are ofconsiderable length and subjected to thermal change or forces, such asvibration or frictional drag, which tend to bend or deflect the memberalong its longitudinal axis.

Because of the relatively high cost and difficulty of manufacturingceramic members in continuous lengths, for example lengths greater thanabout two feet, ceramic materials have heretofore been generally limitedto use in those situations where their relatively high cost is justifiedin order to obtain the advantages from the physical and/or chemicalproperties of the ceramic materials. Even in such special situationswhere ceramic lengths have been employed, it has been important toassure that the elongated ceramic members neither bend nor are subjectedto localized stresses, so as to avoid cracking and/or breaking of theelongated member. Consequently, the circumstances under which elongatedceramic members could be used heretofore have been severely limited.

Commonly in papermaking systems, there are two members, one of which ismovable relative to the other and in frictional engagement therewith. Inthese systems, at least one of the members will possess a working orwear surface defining an area of contact between the members. Examplesof such systems include the combination of elongated drainage devices,such as foils or suction boxes, in contact with a forming fabric in aFourdrinier papermaking machine, a Uhle Box which bears against aforming fabric or felt in a papermaking machine, and doctor blades foruse in contact with rotating drums or other moving members. In thesesystems, the member having the wear surface frequently is of elongatedgeometry and has a length as great as 20 to 30 feet, or greater.

In papermaking machines, e.g. a Fourdrinier machine, a twin wiremachine, or the like, a dilute slurry of wood fibers in a water mediumis deposited on a moving screen known in the art as a wire. Water drainsand/or is withdrawn from the slurry and through the openings in the wireto produce a self-sustaining paper web. These wires may be made of ametal or plastic as known in the art.

Various drainage devices have been employed heretofore for aidingwithdrawal of water from the slurry by developing suction on that sideof the wire opposite the slurry carried thereon. Foils are among suchdevices. The usual foil comprises an elongated member, which may be 20or more feet long, that extends transversely of the direction of travelof the wire and serves to support the moving wire incident to its waterremoval function. The usual foil is stationarily mounted beneath thewire by means of a support structure, each end of which is mounted onthe papermaking machine, so that the foil and its support structure isself-supporting along that portion of its length between the endsupports. At least one of the end mountings provides for expansion andcontraction of the foil and its support structure as their lengthschange due to temperature changes as is known in the art.

Foils usually are provided with a top surface having a leading edge(facing the inlet end of the papermaking machine) which scraps waterfrom the bottom surface of the wire, a substantially flat portion whichcontacts and supports the moving wire, and a trailing portion thatdiverges downwardly away from the wire. The action of the wire movingover and past the trailing portion develops a reduced pressure in thearea between the wire and the trailing portion that functions to pullwater from the slurry through the wire. When the foil is geometricallyuniform and free of gaps, cracks or the like along its length, there isan evenly distributed and generally uniform suction developed along thelength of the coil and a uniform withdrawal of water from the slurry.This aids in producing a paper web of uniform quality.

It shall be recognized that there is significant frictional engagementbetween the wire and the foil or supporting structure as the wire movesover the foil. This frictional contact between the wire and the foil isin part due to the suction pulling the wire against the foil. Thesefrictional and hydraulic drag forces increase the wear of both the wireand foil. These forces are aggravated by hydraulic drag forces arisingby reason of water on the surface of the fast moving wire impacting theleading edge of the foil. These latter forces and the frictional forcesare sufficient in magnitude to cause the foil to flex along its length,the direction of such flexing being in the direction of movement of thewire across the foil, i.e. the machine direction. When installing a foilon a papermaking machine, it is not uncommon that the foil be adjustedwith respect to the papermaking machine superstructure so as to alignthe foil with the wire. This may involve the addition of shims whichbring the foil into the desired alignment, involving flexing of thefoil.

In some instances, the wires in papermaking machines are supported byelongated devices disposed beneath and transversely of the direction ofmovement of the wire. Such devices do not necessarily aid in withdrawingwater from the slurry through the wire but are subject to the wear andflexing problems as are foils. Metal foils, as introduced to theindustry, proved unsatisfactory due to excessive wear of both the foiland the wire. It was subsequently suggested that the metal be hardenedor that ceramic inserts to provided in strategic locations of the foil.Neither of these concepts provided a sufficiently smooth surface so thatthe wire was worn excessively. It has also been suggested heretoforethat hard, dense ceramic materials be used in drainage devices forpapermaking machines. These problems relate to the present incapabilityof the industry to fabricate ceramic foils of the required size. In viewof the limitations of the industry, it has been suggested heretoforethat drainage devices for papermaking machines be made of multiplesegments of ceramic materials. Ceramic materials in continuous lengthsare economically prohibitive to manufacture and very susceptible tofracture. Insofar as the use of ceramic segments in drainage devices istaught in the prior art, the concepts are not acceptable for the reasonthat the segments separate from each other when the device deflects oris subjected to thermal change thereby opening up gaps or cracks betweenadjacent segments with resultant nonuniformity of paper quality.

In the usual Fourdrinier papermaking machine, the wet paper web passesfrom the wire section to the press section for further water removal.The transfer of the wet paper web from the wire section to the presssection is frequently accomplished by means of a felt. The paper web,while on the felt, is passed through the press section where additionalfree water is removed from the paper web through the use of variouscombinations of pressure and suction. Following the pressing of thepaper web, it is separated from the felt and passed to furtherprocessing stations. The felt normally comprises an endless fabric sothat as it is separated from the paper web following pressing, thefabric is caused to traverse several return rolls to be directed back tothe point where the wet paper web coming from the wire section isreceived on the felt.

During the time that the paper web is present on the felt and water isbeing removed from the paper web through the felt, the pores in the feltbecome plugged by such materials as rosin, clay, starch, paper fines,bacterial products and so forth. Also, as the felt passes through thepresses, its bulkiness is reduced. To assure uniform porosity of thefelt, hence uniform water removal from the wet paper web, it is desiredthat the felt be cleaned on its return run. Such cleaning is commonlyaccomplished by suction box devices over which the felt is caused tomove during its return run. The suction developed by such box restoresthe bulkiness of the felt as well as cleaning and drying the felt.Suction boxes of this type are also useful in the wet end of aFourdrinier papermaking machine where they are positioned beneath thewire to aid in withdrawing water from the paper slurry carried by thewire. For purposes of this disclosure, the term "fabric" is consideredto include felts and/or wires.

In one common suction box of the type used for cleaning felts, there isprovided an elongated slot which extends the width of the felt so thatas the felt moves transversely across the slot, the desired cleaning andrenewal of the felt is brought about. In an effort to reduce the wear onthe felt and those portions of the suction box which are contacted bythe felt, particularly the edges of the slot in the suction box, it hasbeen proposed that the slot edges be provided with ceramic faces,comprising continuous lengths of ceramic material or adjacent ceramicsegments in side-by-side relation, which provide a smooth, hard and longwearing surface in contact with the felt.

For reasons of economy, only those portions of these and other suctionbox drainage devices in contact with the felt or wire are made ofceramic material. The remainder of the box is made of materials that areless expensive and less costly to fabricate, such other materials,stainless steel for example, providing support for the ceramic portionswhich are securely mounted thereon. As noted above, inasmuch as theceramic and nonceramic materials have different coefficients of thermalexpansion, in the instance of the prior art devices having ceramicsections in side-by-side relation along the edges of the box slot, thethermal changes normally encountered in papermaking machines cause thesupport to expand to a greater degree than the ceramic so that theceramic segments no longer remain in abutting relation and become freeto physicaly separate. Such physical separation produces gaps in thesurface of the box over which the felt or wire moves which causeirregular patterns of air or water flow that manifest themselves insimilar irregularities in the felt surface or in the paper web formed onthe wire. Further, the edges of the gaps between stress or wear pointsthat cause inordinate wear of the felt or wire.

In the instance of continuous lengths of ceramic materials providedalong the edges of the box slot, frictional and/or hydraulic drag forcesarising by reason of the felt or wire moving across the box flex the boxalong its longitudinal axis and cause the continuous lengths of ceramicto crack or break transversely thereof. This develops the undesirablegaps and/or points of wear referred to above so that these prior artdevices also are unsuitable.

Still further, in certain papermaking systems the paper web from thepress section is fed over a cylindrical dryer such as the well-knownYankee Dryer for further drying of the web. In these systems the web istrained about a portion of the peripheral surface of the dryer and driedby heat transferred through the cylindrical shell thereof. Steamintroduced into the interior of the dryer shell is commonly used to heatthe shell. The dry paper web is doctored from the shell by means of adoctor blade comprising an elongated blade member extending transverslyof the direction of the rotation of the dryer and frequenctly in contactwith the exterior cylindrical surface of the dryer along a lineextending across the dryer surface substantially parallel to therotational axis of the dryer. In operation of these dryers, the surfaceof the dryer shell becomes irregular due to it being heated by thesteam. In order to keep the doctor blade in contact with the shell fordoctoring the web from the shell, it is necessary to bend the doctorblade so that if conforms to the irregularities from the shell surface.In this and other systems of this type, it is desired that the elongatedblade member be flexible and have a good wear surface.

It is therefore an object of the present invention to provide anelongated flexible ceramic member useful in a papermaking system. It isalso an object of this invention to provide an elongated flexibleceramic member of substantial length wherein the member comprises aplurality of ceramic segments adapted to accommodate conditions ofthermal change or bending of the member within predetermined limits.Another object of this invention is to provide a method for themanufacture of an elongated flexible ceramic member.

It is also an object of this invention to provide a papermaking systemcomprising at least two members one of which is movable with respect tothe other and in frictional engagement therewith and one of which is anelongated flexible ceramic member.

It is also an object of the present invention to provide a flexible foilor like elongated supporting structure for the wire of a papermakingmachine which affords the advantages of having a hard, long-wearing,smooth surface in contact with the wire. It is also an object of thisinvention to provide a foil including ceramic material at least in thewire-contacting portion thereof, it is another object of this inventionto provide a foil including a plurality of ceramic segments disposed inface-to-face relation to define an elongated foil which is relativelyflexible along its longitudinal axis and wherein gaps do not developbetween the faces of adjacent ceramic segments when the foil issubjected to thermal change or bending movements.

It is also an object of the present invention to provide a slotteddrainage device, particularly useful in a papermaking machine, overwhich the felt or wire of a papermaking machine passes transverslythereof, wherein the longitudinal edges of the slot each include aplurality of ceramic segments disposed in face-to-face relation.

Other objects and advantages of the invention will be recognized fromthe following description and claims, including the drawings in which:

FIG. 1 is a representation, in perspective and partly cut-away, of afoil embodying various features of the invention;

FIG. 2 is an enlarged fragmentary view, part in section, showing aportion of the foil of FIG. 1;

FIG. 3 is an end view, partly cut-away, of the foil shown in FIG. 1;

FIG. 4 is a representation of a segment of the foil shown in FIG. 1;

FIG. 5 is a front view of the segment shown in FIG. 4;

FIG. 6 is a representation, part in section of a slotted drainage deviceembodying various features of the invention;

FIG. 7 is an end view, part in section, of the drainage device of FIG.6.

FIG. 8 is a fragmentary side view of the drainage device of FIG. 6;

FIG. 9 is a fragmentary side view of an assemblage of ceramic segmentsas disclosed herein; and,

FIG. 10 is a fragmentary representation of a support cradle for anassemblage of ceramic segments as disclosed herein;

FIG. 11 is a representation of an elongated segmented ceramic doctorblade member embodying various features of the invention;

FIG. 12 is a representation of a segment of the member shown in FIG. 11;

FIG. 13 is a representation of one embodiment of a system including atleast two relatively movable members and showing various features of theinvention.

FIG. 14 is a grossly exaggerated representation of a plurality ofsegments deflected in a manner to aid in explaining certain calculationsattending the disclosed invention; and

FIG. 15 is a grossly exaggerated representation of a portion of adeflected composite of ceramic segments.

In accordance with the present disclosure, there is provided a systemthat includes two relatively movable members, one of which comprises anelongated ceramic composite. The ceramic member is formed from aplurality of segments, each having opposite flat faces that are alignedwith their flat faces in abutting face-to-face relation, the segementsbeing held in their abutting relation by tension means which maintainsthe segments in compression such that the abutting segment faces do notseparate and form a gap or gaps therebetween when the member issubjected to flexing forces or to thermal change.

FIGS. 1-5 depict a system including a foil 10 positioned transversely ofand in contact with the wire 15 of a papermaking machine which movesthereacross with the front edge 13 of the foil in contact with the wire.The foil includes a trailing edge 17 which diverges from the wire toform an acute angle therebetween. It has been found that the foil can beprovided with the desirable wear characteristics of a ceramic materialand also be made sufficiently flexible to enable the foil to withstandthe maximum deflection of the foil anticipated in a papermaking machine.In the present disclosure, the specific reference is not to beconsidered as limiting the invention but it is recognized that thedisclosed concepts are applicable to relate or similar two-membersystems.

The illustrated foil 10 comprises a support structure 11 on which thereis mounted an assemblage 14 of ceramic segments or wafers 12, each beingof generally rectangular geometry and having two opposite parallel faces16 and 18. The segments are disposed in face-to-face relation with theirparallel faces abutting the parallel faces of adjacent segments todefine an elongated assemblage 14 of a length sufficient to extend fullyacross the width of the wire 15 moving across the foil. As will appearhereinafter, the abutting faces of adjacent segments are subjected to acompressive force applied at substantially right angles to the faces. Toprevent cracking or breaking of the segments due to unevenly appliedstresses, the faces 16 and 18 are each substantially flat and areoriented substantially parallel to each other and substantiallyperpendicular to the longitudinal axis of the assemblage 14. Each of theparallel faces is flat and smooth to within less than about 20microinches (AA) so that when the individual segments are placed inface-to-face relation, the abutting flat faces of adjacent segments liein contact with each other over substantially the entire areas of theabutting faces without significant open space therebetween. An opening20 extending between the opposite flat faces 16 and 18 of each segmentis aligned with similar openings of the abutting segments to provide achannel 22 through the assemblage.

Each illustrated segment further includes a flat top surface 26, a flatbottom surface 28, and forward and rear surfaces 30 and 32,respectively. The forward surface 30 extends upwardly from the bottomsurface 28 to join the forward edge of the top surface 26 and define anacutely angled leading edge 34. As indicated, the top surface 26 of eachsegment is flat. The rear edge of such flat surface 26 transists into adiverging trailing surface 36. In the illustrated segments, the trailingsurface 36 is generally arcuate to provide an increasingly greater acuteangle between the trailing surface 36 and the Fourdrinier wire 15passing over the foil (see FIG. 3). It may be desired in certainapplications to not use the foil in withdrawing water, in which case theentire top surface of each segment may be flat. Alternatively, thetrailing surface 36, itself, may be substantially flat so as to form aconstant angle with the wire.

In producing a foil of given length, a sufficient number of segments 12are assembled in face-to-face relation with their respective openings 20aligned to obtain the desired foil length. The assembled segments aresecured together with a force applied substantially in the direction ofthe length of the assemblage 14 and substantially perpendicular to theflat parallel faces of the segments. This force is sufficient to placethe segments in elastic compression and is suitably applied as by atension means applying a compressive force to opposite ends 37 and 39 ofthe assemblage 14. One suitable tension means is a cable 24 insertedthrough the aligned openings 20 of the assembled segments, pulled to therequired length, anchored at the opposite ends of the assemblage as byswage fittings 41, and released to exert a compressive force to theassemblage at its opposite ends. Alternatively, other tension means maybe used to establish the desired compression of the segments in theassemblage. One such other means includes a rod disposed in the alignedopenings 20 of the segments and fitted with a nut at one or both of itsends so that tightening of the nuts tensions the rod and places thesegments in compression. One suitable cable for applying the desiredcompression force to the segments is made of carbon steel and of thegeneral type employed in prestressed concrete structures.

The cable 24 may be chosen with a diametral dimension less than thediametral dimension of the opening 20 in each segment and after thesegment is in place on the cable the space between the cable and theinside surface of the opening 20 in the segment may be filled with agrout 44, such as rigid polyurethane, to position the cable within theopenings 20 and provide added assurance that the segments do not rotateabout the cable and that the faces of adjacent segments remain flushwith each other. One suitable grout is a liquid casting urethane polymerdesignated as LD-2699, sold by E. I. Du Pont de Nemours Company,Trenton, N.J. This grout also accommodates the axial movement of thesegments with respect to the compression cable during compression of thestacked array.

In one embodiment, the assemblage of segments is provided with a plateor other means such as a metallic segment 40 at each end of theassemblage to provide for distribution of the compressive force over theface of each end segment to protect it from destruction by localizedforces. A plurality of tension means may be employed to force thesegments into the desired compression and in those instances where thedesired compression is relatively great, such provide greatercompression capability. Multiple, spaced apart, tension means also aidin more evenly distributing the compressive forces over the abuttingfaces of the segments.

In the assemblage 14 of segments, the individual segments 12 areoriented with respect to each other in a manner such that their commonsurfaces lie in common planes to combine with each other to define anelongated substantially flat top surface 46 extending along the lengthof the foil and adapted to contact and support a Fourdriner wire 15moving thereacross. The combined aligned faces also define an elongatedtrailing surface 48 which is a continuation of the flat surface 46 butdiverges downwardly away from the wire 15 to define a generallytriangular (cross-section) zone 50 between the trailing surface 48 andthe Fourdrinier wire 15. It is in this zone 50 that the usual relativelylow pressure is developed which assists withdrawal of water from aslurry of paper fibers carried on the wire. The elongated assemblage 14of ceramic segments further includes an inclined forward surface 52,defined by the combined forward faces of the segments, that joins theforward edge of the flat top surface 46 to define an acutely angledleading edge 13 extending the length of the foil and which functions toscrape water from the wire as it moves past the stationary foil.Alignment of the segments so that their common surfaces combine toprovide the described foil surfaces is accomplished during assembly.

In the illustrated foil 10, the stack 14 of ceramic segments 12 ismounted in a support saddle 56 which in turn is mounted on existingsuperstructure of a usual Fourdriner papermaking machine (not shown).Such papermaking machines, their structure and operation, are well knownin the art and need not be discussed herein. Preferably, the supportsaddle 56 is removably secured in position on the papermaking machine asby means of bolts 60 that join the support saddle at spaced apartlocations to an elongated bar 58 that extends between opposite sides ofthe papermaking machine and which is itself secured at its opposite endsto the papermaking machine. The support saddle 56 and the bar 58, beingsecurely joined to each other at relatively closely spaced points,exhibit thermal expansion characteristics that are some combination ofthe individual thermal characteristics of the saddle 56 and bar 58. Itwill be recognized that if the saddle and bar are of the same material,they will exhibit the thermal expansion characteristic of such material.

The support saddle 56, in the illustrated foil, includes an elongatedbottom portion 82 in FIG. 1 which resides on and is bolted to the bar 58to join the saddle to the bar referred to above. A rear wall portion 64,formed integrally with the bottom portion, extends upwardly from thebottom portion 62 of the saddle. The upper surface 66 of the bottomsection 62 and the forward surface 68 of the rear wall 64 receives thebottom surfaces 28 and at least a portion of the rear surfaces 32 of thestacked segments to provide support for the segments and position themfor engagement with the wire 15. At the juncture of its surface 66 andits surface 68, the support saddle is cut away along its length toaccommodate the bottom rear corners 70 of the segments. In theillustrated support saddle, these surfaces 66 and 68 define an acuteangle therebetween into which the corners 70 of the segments fit therebyrestraining the segments against upward movement out of the supportsaddle. Further support and retention of the segments in the saddle 56is provided by a plurality of clamps 72 that are removably attached asby bolts 74 to the bottom portion 62 of the saddle at locations spacedalong the length of the foil. A generally semicircular (cross-section)groove 76 extending parallel to the longitudinal axis of the foil isprovided on that face 78 of the clamp next to the segments. A similargroove 80 is provided on the forward face of each segment so that thetwo grooves define a generally circular channel between each clamp andthe segments faced by the clamp. A relatively non-yielding cylindricalrod 82 is fitted into the channel defined by the grooves 76 and 80 toprevent movement of the segments with respect to the clamps 72 andthereby hold the segments in position in the saddle 56.

A further system including a drainage device specifically a Uhle box),for papermaking is shown in FIGS. 6-10 and this system comprises asuction box having a longitudinal slot 100 whose longitudinal side edgeseach comprise a plurality of ceramic segments 102 disposed inface-to-face relationship and held together in an assemblage 104 in thedirection of their composite length with a force sufficient to hold thesegments in elastic compression to the degree sufficient to accommodateanticipated thermal change and/or flexing without physical separation ofthe segments. This is accomplished by forming the side edges of the slot102 in the suction box 106, from the respective assemblages 104 and104', each of relatively thin ceramic segments 102 held together bymeans of a nonceramic tension means 120 with a compressive force appliedin the direction of their composite length.

Various drainage device, e.g., Uhle boxes, suction boxes, etc. may besupplied with ceramic edges along the sides of the slot therein asdisclosed herein. For simplifying the present disclosure, the discussionat times refers to a suction box, but such is not to be deemed to limitthe invention.

With reference to FIGS. 6-10, in one embodiment the suction box 106includes a generally elongated tubular housing 108 having a slot 109 cutin one of its walls 110 so that the slot opens facing a felt 112 or thelike which moves transversely over the slot. Each of the longitudinalside edges of the slot 100 comprises an assemblage 104 including aplurality of ceramic segments 102 held in face-to-face relation toprovide ceramic surfaces 114 and 116 in contact with the felt 112. Eachof the ends of the box is closed as by a plate 118, at least one ofwhich has an outlet conduit 122 leading to a source of suction (notshown) by means of which a vacuum is developed within the box. The twoassemblages 104 and 104' of ceramic segments face each other and definean extension of the slot 109 in the box. As desired, each end portion124 of the slot 100 may be sealed as by means of a deckle 126 whoseconstruction and function is known in the art.

The suction box 106 is supported at its opposite ends on exitingpapermaking machine superstructure 128, the box being disposed on oneside of the felt with the felt bearing against the ceramic surfaces asit moves transversely over the box. The vacuum developed within the boxpulls water and other material, such as felt contaminates, from thefelt.

It will be recognized that the suction developed within the box pullsthe felt against the ceramic surfaces 114 and 116 thereby increasing thefrictional drag of the felt against the box. These frictional forces areaggravated by hydraulic drag forces such as are developed by waterdroplets on the the fast moving felt or wire impinging the leading edgeof the box. Such friction and hydraulic drag forces bend the box alongits longitudinal axis in the direction of felt or wire travel.

As noted, the suction box is subject to exposure to thermal changes suchas may occur during shipment or storage, as well as the difference inthe temperature of the box at the time it is installed on thepapermaking machine and its temperature when the papermaking machinereaches its operating temperature.

In the illustrated suction box 106 each of the assemblages 104 and 104'comprises a plurality of ceramic segments or wafers 102, each beinggenerally disc-shaped and having two opposite parallel faces 130 and132. The segments are disposed in face-to-face relation with theirparallel faces abutting the parallel faces of adjacent segments todefine the elongated assemblage 104, the number of segments in theassemblage being sufficient to provide a length sufficient to extendfully across the width of a felt 112 moving across the box. Abuttingadjacent segments are subjected to a compressive force applied atsubstantially right angles to their parallel faces. To prevent crackingor breaking of the segments due to unevenly applied stresses, the faces130 and 132 are each substantially flat and are oriented substantiallyparallel to each other and substantially perpendicular to thelongitudinal axis of the assemblage 104. Each of the parallel faces isflat and smooth to within less than about 20 microinches so that whenthe individual segments are placed in face-to-face relation, theabutting flat faces of adjacent segments lie in contact with each otherover substantially the entire areas of the abutting faces withoutsignificant open spaced therebetween. An opening 134 extending betweenthe opposite flat faces 130 and 132 of each segment is aligned withsimilar openings of the abutting segments to provide a channel throughthe assemblage.

The ceramic composite of this embodiment is produced in like manner asthe foil referred to hereinbefore, that is a sufficient number ofsegments 102 are assembled in face-to-face relation with theirrespective openings 134 aligned to obtain the desired length. Theassembled segments are secured together with a force appliedsubstantially in the direction of the length of the assemblage 104 andsubstantially perpendicular to the flat parallel faces of the segments.This force is sufficient to place the segments in elastic compressionand is suitably applied as by a tension means applying a compressiveforce to opposite ends 136 and 138 of the assemblage 104. The twoassemblages 104 and 104' are substantially identical. One suitabletension means is a cable 140 inserted through the aligned openings 134of the assembled segments, pulled to the required length, anchored atthe opposite ends of the assemblage as by swage fittings 142, andreleased to exert a compressive force to the assemblage at its oppositeends. Alternatively, other tension means may be used to establish thedesired compression of the segments in the assemblage. One such othermeans includes a rod disposed in the aligned openings 134 of thesegments and fitted with a nut at one or both of its ends so thattightening of the nuts tensions the rod and places the segments incompression. One suitable cable for applying the desired compressionforce to the segments is made of carbon steel and of the general typeemployed in prestressed concrete structures.

The cable 140 may be chosen with a diametral dimension less than thediametral dimension of the opening 134 in each segment and after thesegment is in place on the cable the space between the cable and theinside surface of the opening 134 in the segment may be filled with agrout 144, such as rigid polyurethane, as described hereinbefore. Theend segments may be protected from localized forces by a plate ormetallic segment 146, and plural tension means may be employed aspreviously described.

In the assemblage 104 of segments, the individual segments 102 arealigned with respect to each other in a manner such that theirperipheries are flush with each other to define an elongated top surface114 extending along the length of the box and adapted to contact andsupport a drier felt or Fourdrinier wire moving thereacross. Employingcenterless grinding techniques, the aligned peripheries of the segmentsare provided with a collective smooth surface finish of less than about20 microinches AA (arithmetic average) so as to provide for lowfrictional contact between the ceramic surfaces 114 and 116 and the felt112. In this manner, the wear of the ceramic surfaces and the felt isminimized. It has also been found that less horsepower is required tomove the felt over the disclosed ceramic surfaces than has heretoforebeen required with accompanying savings in power. In the depictedsuction box, the assemblages 104 and 104' of compressed ceramic segmentsare mounted on ledges 148 and 150 of the upper wall 110 of the suctionbox 106. One suitable mounting is depicted in FIGS. 6 and 10 andcomprises elongated cradles 152 and 154, one on each side of the slot100. Each of the depicted cradles includes a first continuous lengthclamp 156 extending over substantially the entire length of the sideedge of the slot 100 and shaped to receive an assemblage of segments104' therein. The fit between each continuous clamp and its assemblageof segments along the length of the clamp is sufficient to form a vacuumseal therebetween. If necessary or desired a gasket may be employedbetween each assemblage and its respective cradle. The assemblage 104 isretained in its continuous clamp 156 means of a plurality of furtherclamps 158 each having a concave face 160 contacting the assemblage andbeing removably secured to the continuous clamp as by means of bolts162. In addition to holding the assemblage in place, these furtherclamps 158 force the assemblage against the continuous length clamp 154to aid in developing and maintaining a vacuum seal between theassemblage.

The continuous surfaces 164 and 166 of the clamps 152 and 154 aredisposed facing each other to define an elongated extension of the slot100 so that fluid or other matter withdrawn from the felt or wire isdirected into the suction box to be discharged through the conduit 122.Each of the continuous length clamps 152 and 154 is removably mounted onits respective ledges 148 and 150 as by screws 168. As necessary, agasket material 170 is positioned between each clamp 154 and itssupporting ledge 150 to form a vacuum seal therebetween.

One embodiment of a system which includes an elongated flexible ceramicmember and which includes at least two members, one of which is movablerelative to the other and in frictional engagement therewith is thedoctor system depicted in FIGS. 11-13. This depicted system includesYankee Dryer 200 on which a paper web 202 is dried and creped. The webis trained about a portion of the peripheral surface of the dryer 20 anddried by heat transferred through the cylindrical shell 204 thereof.Steam introduced into the interior of the dryer shell is commonly usedto heat the shell. The paper web 202 is doctored from the shell 204 bymeans of a doctor blade 206 as is well known in the art to provide acreped paper web 208. In this embodiment, the dryer shell 204 comprisesa first member of the system and is movable relative to and infrictional engagement with the doctor blade 206 which comprises a secondmember of the system.

In the system depicted in FIG. 13, the doctor blade 206 is positionedwith respect to the dryer surface 204 and to the paper web 202 bysupport means shown generally at 210 including a pair of jaws 212 and213 having shoulders 214 and 215, respectively, that engage mating slots216 and 217 in opposite surfaces of the doctor blade 206. Other suitablemounting means will be readily recognized by one skilled in the art.

In operation of the depicted system, the surface of the shell 204becomes irregular due to its being heated by the steam. In order to keepthe doctor blade in contact with the shell for doctoring the web fromthe shell, it is necessary to bend the doctor blade so that it conformsto the irregularities in the shell surface.

In these and other systems of this type, as disclosed, it is desiredthat one of the members be flexible and have a good wear surface that isengaged by the other of the members. It has long been desired that suchone of the members be made of a ceramic material to take advantage ofthe wear resistance of this material. Continuous lengths of ceramic areprohibitively costly. Members having small ceramic inserts disposedalong the length of the member to define a wear surface have been triedbut such members develop gaps between the inserts where the member bendsduring use so that the edges and/or corners of the separated segmentsbecome points of excessive wear.

The illustrated doctor blade system comprises an elongated flexiblemember including a plurality of ceramic segments 220 each having atleast two opposite substantially parallel flat faces 224 and 226 (FIG.12). Each of the depicted segments 220 further includes an upper flatsurface 230 which joins a forward upright surface 232 to define aleading edge 234, and an opening 236 extending through each segmentbetween its opposite flat surfaces 224 and 226. A plurality of thesesegments are assembled in face-to-face abutting relationship with theirleading edges aligned to define the doctor blade 206. As illustrated,the flat faces 224 and 226 of each segment are disposed substantiallyperpendicular to the longitudinal axis, i.e. the composite length, ofthe composite member. The aligned segments 220 are forced toward eachother by a tension means 238, anchored to opposite ends of thecomposite, with a force which elastically compresses the segments.

Each of the segments of each of the elongated members of the presentdisclosure is fabricated from a hard dense ceramic material that isavailable at a reasonable cost.

The ceramic preferably is an impervious crystalline material thatcombines high mechanical strength with extreme hardness, inertness,refractoriness, and high chemical resistance properties. Because theseproperties are retained over a wide range of application andenvironmental conditions that many other materials cannot withstand,such ceramics suitably serve under conditons adverse to other materials.Alumina, silicon carbide, boron carbide and silicon nitride materialspossess those properties required in many industrial applications, andeconomically feasible for such end uses. Alumina is particularlysuitable and is preferred for use in the present ceramic member becauseof its properties and its availability at relatively low cost whenformed in relatively short segments.

The alumina segment is formed by compacting finely ground oxide powderswith fluxing agents and inhibitors at relatively high pressures as isknown in the art. Forming methods include dry pressing, isostaticpressing, casting, extrusion, and injection molding. After forming, theresulting "green" ceramic segment is fired at a high temperature for aspecific length of time. Firing temperatures vary but usually rangebetween 2,500° F. and 3,250° F. During firing the ceramic shrinks;therefore, segments are formed while in the green state to allow for thephysical reduction caused by firing. After firing, the ceramic segmentis strong, hard and dense, composed substantially of pure alumina ofcontrolled crystal size. Machining of the ceramic segments is possibleeither before or after firing. Fired segments are ground or lapped toobtain the desired surfaces thereof. Grinding usually must be done withdiamond-impregnated wheels, although silicon-carbide or alumina wheelsare sometimes used.

Most of those physical properties desired in the ceramic segmentsimprove as the purity of the ceramic increases, especially hardness,compressive strength, wear resistance and chemical resistance. Forexample, alumina ceramic compositions having aluminum oxide contentsless than about 85% lose certain of their properties to an unacceptabledegree. Preferably, the alumina ceramics contain about 90.0 percent ormore aluminum oxide.

The compressive strength of the ceramics exceed that for most materials.For example, compressive strengths as high as 550,000 psi have beenobtained in certain relatively pure alumina ceramics. Suitablecompressive strengths for the ceramic segments range upwardly from about200,000 psi.

Each of the segments is provided with two opposite substantially flatand parallel faces. The segments are disposed in face-to-face relationwith their parallel faces abutting the parallel faces of adjacentsegments to define the elongated composite of a desired length andsubjected to a compressive force applied at substantially right anglesto the faces. The flatness and parallelism of the abutting segment faceshelp to prevent cracking or breaking of the segments due to unevenlyapplied stresses or localized stresses by distributing the compressiveforces evenly over the abutting faces. Abutting segment faces, each ofwhich is flat to within about 0.0002 inches and has a surface finish ofless than about 20 microinches arithmetic average (AA) have been foundto be suitable for these purposes. When such individual segments areplaced in fact-to-face relation without grout or adhesive, the abuttingflat faces of adjacent segments lie in intimate contact with each otherover substantially the entire areas of the abutting faces withoutsignificant open space therebetween so that the abutting faces supplysupport to each other especially when the surface of the member is beingground as will be described hereinafter. In one embodiment, each segmentis provided with an opening extending between the opposite flat facesthereof. This opening in a segment is aligned with similar openings ofabutting segments to provide a channel through the composite forreceiving a tension means for compressing the segments in the directionof their composite length.

As noted above, in producing an elongated member of given length, asufficient number of segments are assembled in face-to-face relationwith their respective openings aligned to obtain the desired length. Theassembled segments are secured together with a force appliedsubstantially in the direction of the length of the composite andsubstantially perpendicular to the flat parallel faces of the segments.This force is sufficient to place the segments in elastic compression,and produce a significant compressive strain, and is suitably applied asby a tension means applying a compressive force to opposite ends of thecomposite. One suitable tension means is a cable inserted through thealigned openings extending between the opposite faces of each of theassembled segments, pulled to the required length, anchored at theopposite ends of the composite as by swage fittings to exert acompressive force upon the composite at its opposite ends.Alternatively, other tensioning means may be used to establish thedesired compression of the segments in the composite. One such othermeans includes a rod disposed in the aligned openings of the segmentsand fitted with a nut at one or both of its ends so that tightening ofthe nuts tensions the rod and places the segments in compression. Onesuitable cable for applying the desired compression force to thesegments is made of carbon steel and of the general type employed inprestressed concrete structures.

The cable may be chosen with a cross sectional area less than the crosssectional area of the opening in each segment and after the segment isin place on the cable the space between the cable and the inside surfaceof the opening in the segment may be filled with a grout 44 (FIG. 2)such as rigid polyurethane, to position the cable within the openings.One suitable grout is a liquid casting urethane polymer designated asLD-2699, sold by E. I. Du Pont de Nemours Company, Trenton, N.J. Thisgrout also accommodates the axial movement of the segments with respectto the compression cable during compression of the composite and/orrelative movement between the segments and the cable in the event themember is subjected to thermal change during use.

As illustrated, the composite of segments may be provided with a plateor other means such as a metallic segment at each end of the compositeto provide for distribution of the compression force over the face ofeach end segment to protect it from damage by localized forces. In thoseinstances where the desired compression is relatively great a pluralityof tensions means, e.g. cables, provides greater compressive capability.In that event, the plurality of cables are desirably threaded throughspaced apart, aligned openings through the segments. Such constructionaids in more evenly distributing the compressive forces over theabutting faces of the segments.

The flexibility of the ceramic member is made possible be employingrelatively short segments (e.g. on the order of 1 inch long) heldtogether with a compressive force such that when the elongated compositedeflects by a distance d, along its length (see FIGS. 14-15), at least apart of the compression, e.g. compressive strain, in those portions 240and 242 of the abutting faces 244 and 246 of adjacent segments disposedon the outside of the line of curvature A of the deflected composite isrelieved, permitting those portions of the segments to expand toaccommodate the deflection without physically separating. Importantly,the compressive force holding the segments together is less than themaximum compressive strength of the ceramic material by an amount whichpermits those portions 248 and 250 of the abutting faces 244 and 246 ofadjacent segments on the inside of the line of curvature A of thedeflected composite to be compressed by an additional amount, causingthese portions of the segments to compress by an amount sufficient toaccommodate the deflection without destruction of the segments. Inaddition, the length of the individual segments is chosen to besufficiently small as permits their manufacture at minimized coststaking into consideration the anticipated compressive forces to whichthe segments are to be subjected in order to obtain the desired responseof the composite incident to deflective forces.

In addition to the deflective forces, consideration must be given tothermal changes affecting the element in that such will usually producedifferent responses in the ceramic segments and the tension member. Suchthermal changes can arise by differences in the start-up and operatingtemperatures of the machine or system in which the element is installed,and/or changes in ambient temperature of the element during assembly,shipping or installation.

In calculating the compression required to accommodate the maximumanticipated deflection of a member of given length without separation ofthe segments, it is assumed that the deflection of the member will takethe shape of a uniformly loaded simple beam and that the maximumdeflection will be sufficiently small (less than about 1 percent of themember length) to permit the use of calculations based on circular arcs,rather than more exact curves. The latter could be used in thosecircumstances where more exact calculations are required; however, ithas been found that such is not necessary in constructing flexiblemembers for most end uses. More specifically, and with reference toFIGS. 14 and 15, for a ceramic member of given length, l (in inches),having a longitudinal axis subjected to a maximum anticipateddeflection, d (in inches), along a line of curvature A, and made up of aplurality of segments each being of a known .[.length, L (in inches),and a.]. dimension, h (in inches), across the segments, in the directionof the applied deflective force and a cross-sectional area, A_(c), insquare inches, the preloading on the tension member, e.g. cable 24 (FIG.1), which will impart to the ceramic segments the necessary compressiveforce that precludes separation of the segments is calculated using theequation

    P.sub.D = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] (1)

where

E_(c) = the modulus of elasticity of the ceramic;

A_(c) = the cross-sectional area of a ceramic segment in a planeperpendicular to the composite length of the member, in square inches;

d = the maximum anticipated deflection of the member, in inches;

h = the dimension of a ceramic segment in the plane perpendicular of thecomposite length of the member and in alignment with the direction ofthe deflective force, in inches;

l = the overall length of the member. .[., and

L = the length of a ceramic segment, in inches.].

With reference to Equation (1), it is noted that the initiallydetermined preloading is divided by 2 to give the preloading to be usedin tensioning the cable. This fact arises because of the manner in whichthe ceramic segments are stressed when the member is deflected whileunder compression. More specifically, assuming the cable is disposedmidway between the ends of the segment dimension h, when the member isin an undeflected state, the stress on each compressed ceramic segmentis the same at any point along the dimension h. When the member isdeflected, the stress in that portion of a segment on the outside of theline of curvature (on the outside end of the dimension h) is reducedtoward zero and the stress in that portion of the same segment on theinside of the line of curvature is doubled. Thus when preloading thealigned segments, the stress imparted to the segments is taken as theaverage of the stresses along the dimension h when the member isdeflected by a maximum amount.

The effect of thermal change upon the ceramic member must also be takeninto account. Thermal changes occur most frequently by reason of theceramic member being manufactured at a first temperature, roomtemperature for example, and thereafter encountering a substantiallyhigher operating temperature. In such circumstances, the strain in thecable decreases when its temperature increases by reason of the cableexpanding when heated. Expansion of the cable cross-section as well asalong its length is of importance. The ceramic also expands when heated,but usually to a lesser extent than the cable, so that there is added tothe preload calculated for deflection in accordance with Equation (1),an additional preloading which will compensate for the effect of thermalchange upon the cable and the ceramic and provide the desired preloadingfor accommodating deflection up to a maximum temperature. Suchadditional preloading of the tension means is calculated using theequation.

    P.sub.T = [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]                                      (2)

where:

α_(s) = the coefficient of thermal expansion of the tension member;

α_(c) = the coefficient of thermal expansion of the ceramic;

ΔT = degrees of temperature change anticipated, in degrees F;

A_(s) = cross-sectional area of the tension member, in square inches;

E_(s) = the modulus of elasticity of the tension member

A_(c) = the cross-sectional area of a ceramic segment in a planeperpendicular to the length of the member, in square inches;

E_(c) = the modulus of elasticity of the ceramic.

Combining Equations (1) and (2) gives

    P = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] + [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]                                      (3)

where P is the total preloading of the tension member which will preventseparation of the segments of the member 30 when the member is deflectedup to a maximum amount d while at a temperature less than an anticipatedmaximum temperature it will be noted that in those situations where theceramic member will not experience a thermal change, ΔT will be 0 andP_(T) [including its equivalent expression in Equation (3)] will be 0and no additional preloading will be required to account for thermalchanges.

Thus, in any given situation where the elongated ceramic member is to besubjected to deflection forces, it is possible to select a compositewhich exhibits the desired non-separation of abutting segment faces whenthe composite is deflected along its composite length. As shown inEquation (1), the preloading force (compressive force) applied to thealigned segments, for any given maximum anticipated deflection and totallength of the segmented member, depends upon the length of eachindividual segment and the dimension h of each segment. Thus, if thedeflection capability of a given composite of ceramic segments is lessthan that which precludes physical separation of the abutting faces ofthe segments under the anticipated deflection, an adjustment can bemade, in many instances, in either the length or width of the individualsegments, or in both the length and width. Of course, consideration mustbe given to the added compression experienced by those portions of theabutting segment faces disposed on the inside of the line of curvatureof the deflected composite.

The preloading force exerted upon the ceramic segments is kept belowthat amount of force which will compress the ceramic material to withinabout one-half, and preferably to within about 20 percent, of itsmaximum compressive strength to insure that localized stresses which mayoccur within the composite do not exceed such maximum compressivestrength with resultant damage to one or more segments. This preferredpreloading also provides a substantial margin of safety against damageto the segments by inadvertent overloading of the segments to produceundue deflection. In any event, the preloading of the segments issufficient to shorten the length of each segment, hence shorten theoverall length of the composite. Further, in the preferred preloading,the segments are sufficiently deformed at the interface between abuttingsegment faces as results in substantial loss of joint identity at suchinterface. Such deformation is known to occur when the segments arepreloaded to between about 15 and 20 percent of the maximum compressivestrength of the ceramic. This substantial loss of joint identity hasbeen found to be important in establishing the working surface on themember in that such allows the composite to be ground to a suitablesmoothness. Less preloading is acceptable but at a loss of certainty ofachieving the desired properties in the composite. Thus, the preloadingof the ceramic segments must be sufficient to maintain the segmentsabutting when the member is deflected by a maximum amount d but lessthan that preloading which will compress the ceramic to more thanone-half its total compressive strength.

It is understood that in the present discussion each of the segments issubstantially identical to each other segment in a given composite. Suchis assumed for purposes of simplifying the disclosure. It is notrequired, however, that all of the segments be identical. For example,it may be desirable to provide a segmented member which is deflected bydifferent degrees along its length. In such an embodiment, thedeflective characteristics of the member will differ in differentportions of its length and the segments in each such portion may differin length from the segments in other portions of the length of themember.

As disclosed, one of the members of the system is movable with respectto the other member. In many embodiments, one member is held stationarywhile the other member moves thereover in frictional engagementtherewith. Similarly, in many embodiments the stationary member will bethe flexible ceramic member and will include a leading edge which isinitialy contacted by the moving member as it moves over the ceramicmember. In such instances it is important that such leading edge bestraight and free of irregularities such as gaps resulting from chippingof the leading edge inasmuch as such irregularities, among other things,hinder or prevent alignment between the two members and create wearpoints between the moving members.

The segmented ceramic member, being intended for use in a system whereit is in frictional engagement with a further member and there isrelative movement between the members, is provided with an elongatedsmooth working surface (surfaces 46, FIG. 3; surfaces 114 and 116, FIG.6; surface 230, FIG. 11). This surface extends along the length of theceramic member and defines an extended area of contact between therelatively moving members. Minimum wear of this surface and of the otherof the moving members is obtained by maximizing the smoothness of thisworking surface. This is accomplished by grinding the working surfaceafter the segments have been formed into the composite and preloaded asdescribed hereinabove.

In a typical grinding operation the segmented ceramic member is anchoredon the bed of a grinding machine. A diamond impregnated grinding wheel,preferably of the type having an annular planar grinding surface is usedin the grinding process. This grinding wheel is moved into contact withthe segmented member with the plane of the grinding surface of thegrinding wheel disposed at a slight angle with respect to the plane ofthe surface to be ground so that only a portion of the rotating grindingsurface is in contact with the segments at a given time. Preferably thegrinding surface plane is also disposed with respect to the workingsurface so that grinding of the surface takes place as the annulargrinding surface moves onto the surface and little or no grinding takesplace as the grinding surface is moving away from the surface beingground.

The rotation of the grinding wheel, when grinding a leading edge of thetype shown in FIG. 1, is such that the grinding surface initiallycontacts the leading edge, e.g. edge 13 of FIG. 1, as the grindingsurface moves toward the edge. In this manner, the grinding forcesexerted upon the segments are directed inwardly of the segments to aidin preventing chipping of the segments edges during grinding.Preferably, the grinding action at the leading edge is in a directionsubstantially perpendicular to the leading edge. Variations of greaterthan about 10° from such perpendicular relationship may providerelatively poor edges.

In the grinding operation the compression of the segments in thedirection of their composite length maintains the edges of abuttingsegments in supporting relationship to each other. In addition to thisphysical support of one segment by its neighbor, the compression in thesegments is sufficient to prevent the force of the grinding operationfrom placing the segment edges in tension as the grinding wheel dragsacross the segment, thereby enhancing the resistance of the segments toedge chipping during grinding.

EXAMPLE I

The manufacture of a doctor blade is described hereinafter asillustrative of the manufacture of the disclosed composite ceramicmembers of the systems described herein. Doctor blades for doctoring apaper web from the surface of a cylindrical dryer shell normally aredeflected by different amounts along different portions of their lengthdue to undulations in the dryer shell across its width. In making aceramic composite doctor blade the most severe anticipated deflection ischosen and the total deflection capability of the blade is madesufficient to accommodate such. In this Example the length, l, of thechosen deflected portion is 50 inches.

The doctor blade in the configuration illustrated in FIG. 1 is made from1 inch long .[.(L).]. alumina segments (AD-995 from Coors Porcelain Co.)each having a cross-sectional area (A_(c)) of 0.78 square inches. Thedimension (h), the dimension in the direction of the application of thedeflective forces, is 0.875 inch. These segments are aligned with theirflat parallel faces abutting and compressed in the direction of theircomposite length by a stainless steel cable of 0.14 square inchescross-sectional area threaded through aligned openings in the segments.

The maximum anticipated deflection of the doctor blade over the chosen50 inch length, l, is determined to be 0.027 inch and the anticipatedthermal change is from 70° F to 300° F. (ΔT = 230° F). The preloadingfor the cable which passes through the segments is calculated usingEquation (3) as follows: ##EQU1## P = 1579.5 + 2385.19 P = 3964.69pounds

This preloading imparted a compressive force to the ceramic which isabout 1.54 percent of the 330,000 psi approximate maximum compressivestrength for AD-995 alumina. This degree of compression provides for theanticipated deflection, occurring at a temperature of 300° F., withoutcomplete relief of the compression in those portions of the abuttingsegment faces furtherest from the longitudinal axis of the member alongwhich the deflection occurs and, importantly, provides for additionalcompression of those portions of the abutting segment faces nearest thelongitudinal axis of the member as necessary to accommodate thedeflection.

The working surface 230 of the segmented member 222 is ground while themember is supported along its entire length on the bed of a grindingmachine. A 220-grit diamond impregnated wheel, having an annulargrinding surface, as sold by the Norton Company is employed in thegrinding operation. The grinding wheel has a diameter of 10 inches, andis rotated at approximately 3,600 revolutions per minutes. The wheel ismoved along the length of the working surface at a speed between about10 and 20 feet per minute. The position of the grinding wheel relativeto the working surface and its rotational movement is as describedabove. The grinding operation provides a surface finish of about 20microinches (AA) with no significant chipping of the leading edge 234.

EXAMPLE II

Another system of the type disclosed herein comprises a foil and aforming fabric of a Fourdrinier papermaking machine. In this system, theelongated foil is disposed beneath the forming fabric and serves tosupport the fabric and remove water from a slurry of papermaking fiberscarried on the fabric. In these functions, the fabric slides over thefoil while it is pulled against the foil by suction developed by thefoil. There is substantial wear of both the foil and the wire in thesesystems as known heretofore.

A 200-inch long foil for use in a Fourdrinier papermaking machine ismade from 200 l inch long AD-995 alumina segments held in compression bya 0.677 inch diameter stainless steel cable which is passed through anopening located centrally of each segment. Each segment has across-sectional area (A_(c)) of 2 square inches, and a dimension (h) of2 inches. The maximum anticipated deflection of the foil is 0.5 inch andthe anticipated thermal change is from 70° F. to 170° F (ΔT = 100° F).

Using Equation (3), the preloading for the cable for preventingseparation of the segments under such conditions is calcuated asfollows: ##EQU2## P = 10,746 + 3,557.8

P = 14,304 pounds

The preload force in this example stresses the ceramic to 2.17 percentof its maximum compressive strength.

This foil is provided with a ground elongated working surface having asmoothness of less than about 20 microinches AA in the manner disclosedherein. In use, the foil exhibits excellent wear qualities and does notexhibit gaps between abutting segment faces. Foils of this type whenused in a high speed Fourdrinier papermaking machine do not producestreaks in the paper web formed on the forming fabric moving over thefoil, as has been experienced by the prior art segmented foils whichdevelop gaps between abutting segments.

EXAMPLE III

A further system of the type disclosed herein comprises a suction devicefor use in a papermaking machine known as a Uhle Box. This suctiondevice comprises an elongated trough-like device having an elongatedslot extending along its length and opening toward a forming fabric orfelt moving thereacross. A suction is developed within the Uhle Box sothat the fabric or felt is pulled against the edges of the slot andwater or other material is pulled from the fabric or felt into the UhleBox. The edges of the slot are subjected to relatively greater wearforces and the Uhle Box, hence the slot edges, are subjected tosubstantial deflective forces as the fabric or felt moves across thedevice in a direction transverse to its length.

A Uhle Box having each of its slot edges made of a flexible ceramicmember may be fabricated using the teachings of the invention asfollows. Each such slot edge is 200 inches long and made of 1 inch longAD-995 alumina segments held in compression by a stainless steel cablehaving a cross sectional area of 0.25 square inches which is disposed inaligned openings in the segments. Each segment has a cross-sectionalarea (A_(c)) of 0.92 square inch and a dimension of (h) of 1.250 inches.

In calculating the preload for the cable, the maximum anticipateddeflection is 3 inches and the maximum temperature anticipated duringuse is 170° F. The temperature at assembly is 70° F, giving a ΔT of 100°F. Using Equation (3) the preload is determined as follows: ##EQU3## P =18,605 + 1,771.5 P = 20,376.5 pounds

The preload force in this Example stresses the ceramic to 6.71 percentof its maximum compressive strength.

In addition to the advantages of flexibility and resistance to gapingbetween segments, the present ceramic member offers the advantage ofproviding a wear-resistance surface that can be ground smooth to theextent desired. Because the abutting faces of the ceramic segments areheld in exceptionally close contact with each other, when the combinedtop surfaces of the segments are ground smooth, their edges support eachother to prevent chipping of their adjacent edges so that in thefinished surface, even though the dividing line between segments may bevisible as a "hair line" crack, there is no substantial opening or gaptherebetween. The wear surface of the disclosed ceramic member is groundand/or lapped smooth to less than about 20 microinches AA and preferablyto within a few wavelengths of light to provide exeptionallylow-friction contact between the relatively moving members of thesystem. In this manner, the useful lives of both members are prolonged.

While preferred embodiments have been shown and described, it will beunderstood that there is no intent to limit the invention by suchdisclosure, but rather, it is intended to cover all modifications andalternate constructions falling within the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. In a papermaking system including at least twomembers one of which is movable relative to the other and in frictionalengagement therewith, and in which system at least one of said membersis subjected to deflection, the improvement wherein said latter membercomprisesan elongated flexible assemblage including a plurality ofceramic segments, each having at least two opposite surfaces that aresubstantially flat and parallel, said segments being aligned with theirflat faces in abutting face-to-face relation and in respective planesthat are oriented substantially perpendicular to the composite length ofsaid plurality of segements, tension means extending between oppositeends of said assemblage and forcing said segments toward each other in adirection along their composite length and substantially perpendicularto their respective parallel faces with a preload force on said tensionmeans, when said latter member is in an undeflected condition, that isat least the force calculated by the equation:

    P = [(E.sub.c A.sub.c)(8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] + [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]

where: P is the preload of said tension means, in pounds; E_(c) is themodulus of elasticity of the ceramic material; A_(c) is thecross-sectional area of a ceramic segment in a plane perpendicular tothe composite length of said assemblage, in square inches; d is themaximum anticipated deflection of said assemblage, in inches, h is thedimension of a ceramic segment in the plane perpendicular to thecomposite length of said assemblage and in alignment with the directionof said deflective force, in inches;l is the overall length of saidassemblage; α_(s) is the coefficient of thermal expansion of saidtension means; α_(c) is the coefficient of thermal expansion of saidceramic; ΔT is the degrees of temperature change anticipated, in degreesF.; A_(s) is the cross-sectional area of said tension means; E_(s) isthe modulus of elasticity of said tension means, .[.and L is the lengthof a ceramic segment, in inches,.]. but less than the amount of forcewhich will compress said ceramic to over about one-half of its maximumcompressive strength, an elongated smooth working surface extendingalong the length of said latter member and defining an area of contactwith said other member, and means supporting said latter member relativeto said other member with its longitudinal dimension oriented generallytransversely of the direction of relative movement of said memberswhereby loading forces exerted upon said latter member are directedthereagainst in a direction substantially perpendicular to thelongitudinal dimension thereof and deflection of said latter memberpursuant to such loading forces is compensated for in said compressedsegments by further compression of said segments in those portions ofthe abutting faces thereof disposed along the inside of the line ofcurvature of said latter member and by relief of less than all of thecompression in those portions of said abutting faces that are disposedalong the outside of said line of curvature of said member withoutphysical separation of said segments at their abutting faces.
 2. Thesystem of claim 1 wherein said preload force does not exceed a forcewhich will compress said ceramic to greater than about 20 percent of itsmaximum compressive strength.
 3. The system of claim 1 wherein saidworking surface on said latter member includes a substantially straightand continuous leading edge that is in initial contact with said othermember.
 4. The system of claim 1 wherein said tension means forcing saidsegments toward each other is a nonceramic material.
 5. The system ofclaim 1 wherein said ceramic comprises alumina.
 6. The system of claim 1wherein said alumina has a purity of greater than about 85 percent. 7.The system of claim 1 wherein said ceramic segments are substantiallyidentical and each has an opening extending between its opposite flatand parallel surfaces, said openings in said segments being in registerand said tension means extending therethrough.
 8. The system of claim 1wherein each of the abutting flat faces of said ceramic segments is flatto within about 0.0002 inches.
 9. The system of claim 1 wherein saidelongated smooth working surface has a surface smoothness of less thanabout 20 microinches AA.
 10. In a papermaking machine including a movingwire on which a paper web is formed, an improved foil disposed on thebottom side of said wire in frictional engagement therewith comprisinganelongated flexible assemblage including a plurality of ceramic segments,each having at least two opposite surfaces that are substantially flatand parallel, said segments being aligned with their flat faces inabutting face-to-face relation and in respective planes that areoriented substantially perpendicular to the composite length of saidplurality of segments, tension means extending between opposite ends ofsaid assemblage and forcing said segments toward each other in adirection along their composite length and substantially perpendicularto their respective parallel faces with a preload force on said tensionmeans, when said assemblage is in an undeflected condition, that is atleast the force calculated by the equation:

    P = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] + [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]

where: P is the preload of said tension means, in pounds; E_(c) is themodulus of elasticity of the ceramic material; A_(c) is thecross-sectional area of a ceramic segment in a plane perpendicular tothe composite length of said assemblage, in square inches; d is themaximum anticipated deflection of said assemblage, in inches; h is thedimension of a ceramic segment in the plane perpendicular to thecomposite length of said assemblage and in alignment with the directionof said deflective force, in inches; l is the overall length of saidassemblage; α_(s) is the coefficient of thermal expansion of saidtension means; α_(c) is the coefficient of thermal expansion of saidceramic; ΔT is the degree of temperature change anticipated, in degreesF.; A_(s) is the cross-sectional area of said tension means; E_(s) isthe modulus of elasticity of said tension means, .[.and L is the lengthof the ceramic segment, in inches,.]. but less than the amount of forcewhich will compress said ceramic to over about one-half of its maximumcompressive strength, an elongated smooth working surface extendingalong the length of said elongated assemblage and defining an area ofcontact with said moving wire, and means supporting said elongatedassemblage on the bottom side of said moving wire and in frictionalengagement therewith with the longitudinal dimension of said assemblageoriented generally transversely of the direction of movement of saidwire whereby loading forces exerted upon said assemblage are directedthereagainst in a direction substantially perpendicular to thelongitudinal dimension thereof and deflection of said foil pursuant tosuch loading forces is compensated for in said compressed segments byfurther compression of said segments in those portions of the abuttingfaces thereof disposed along the inside of the line of curvature of saidassemblage without physical separation of said segments at theirabutting faces.
 11. In a papermaking machine including a moving fabrichaving a forward direction of motion, an improved elongated drainagedevice oriented transversely of the forward direction of said fabric insupporting contact therewith including a suction chamber and meansdefining a slot along that side of said suction chamber adjacent saidfabric, said slot having closed ends and opposite side edges andextending along the length of said device and being in fluidcommunication with said fabric for the application of suction to thatside of said fabric adjacent said slot, the improvement comprisinganelongated flexible assemblage disposed on each of said side edges ofsaid slot, including a plurality of ceramic segments, each having atleast two opposite surfaces that are substantially flat and parallel,said segments being aligned with their flat faces in abuttingface-to-face relation and in respective planes that are orientedsubstantially perpendicular to the composite length of said plurality ofsegments, tension means extending between opposite ends of saidassemblage and forcing said segments toward each other in a directionalong their composite length and substantially perpendicular to theirrespective parallel faces with a preload force on said tension means,when said latter member is in an undeflected condition, that is at leastthe force calculated by the equation:

    P = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].]+ [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]

where: P is the preload of said tension means, in pounds; E_(c) is themodulus of elasticity of the ceramic material; A_(c) is thecross-sectional area of a ceramic segment in a plane perpendicular tothe composite length of said assemblage, in square inches; d is themaximum anticipated deflection of said assemblage, in inches; h is thedimension of a ceramic segment in the plane perpendicular to thecomposite length of said assemblage and in alignment with the directionof said deflective force, in inches; l is the overall length of saidassemblage; α_(s) is the coefficient of thermal expansion of saidtension means; α_(c) is the coefficient of thermal expansion of saidceramic; ΔT is the degree of temperature change anticipated, in degreesF.; A_(s) is the cross-sectional area of said tension means; E_(s) isthe modulus of elasticity of said tension means, .[.and L is the lengthof a ceramic segment, in inches,.]. but less than the amount of forcewhich will compress said ceramic to over about one-half of its maximumcompressive strength, an elongated smooth working surface extendingalong the length of said assemblage and defining an area of contact withsaid fabric, and means supporting said drainage device relative to saidfabric with its longitudinal dimension oriented generally transverselyof the direction of relative movement of said fabric whereby loadingforces exerted upon said drainage device are directed thereagainst in adirection substantially perpendicular to the longitudinal dimensionthereof and deflection of said assemblage pursuant to such loadingforces is compensated for in said compressed segments by furthercompression of said segments in those portions of the abutting facesthereof disposed along the inside of the line of curvature of saidassemblage and by relief of less than all of the compression in thoseportions of said abutting faces that are disposed along the outside ofsaid line of curvature of said assemblage without physical separation ofsaid segments at their abutting faces.
 12. The drainage device of claim11 wherein said means supporting said assemblage relative to said fabriccomprises an elongated cradle means receiving said assemblage of ceramicsegments in substantially fluid tight relation therewith.
 13. In apapermaking system including a rotating cylindrical member carrying apaper web on the outer cylindrical surface thereof and an elongateddoctor blade disposed adjacent said surface for removing said web fromsaid surface the improvement comprisingan elongated flexible assemblageincluding a plurality of ceramic segments, each having at least twoopposite surfaces that are substantially flat and parallel, saidsegments being aligned with their flat faces in abutting face-to-facerelation and in respective planes that are oriented substantiallyperpendicular to the composite length of said plurality of segments,tension means extending between opposite ends of said assemblage andforcing said segments toward each other in a direction along theircomposite length and substantially perpendicular to their respectiveparallel faces with a preload force on said tension means, when saidassemblage is in an undeflected condition, that is at least the forcecalculated by the equation:

    P = [(E.sub.c A.sub.c ) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].]+ [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]

where: P is the preload of said tension means, in pounds; E_(c) is themodulus of elasticity of the ceramic material; A_(c) is thecross-sectional area of a ceramic segment in a plane perpendicular tothe composite length of said assemblage, in square inches; d is themaximum anticipated deflection of said assemblage, in inches; h is thedimension of a ceramic segment in the plane perpendicular to thecomposite length of said assemblage and in alignment with the directionof said deflective force, in inches; l is the overall length of saidassemblage; α_(s) is the coefficient of thermal expansion of saidtension means; α_(c) is the coefficient of thermal expansion of saidceramic; ΔT is the degree of temperature change anticipated, in degreesF.; A_(s) is the cross-sectional area of said tension means; E_(s) isthe modulus of elasticity of said tension means, .[.and L is the lengthof a ceramic segment, in inches,.]. but less than the amount of forcewhich will compress said ceramic to over about one-half of its maximumcompressive strength, an elongated smooth working surface extendingalong the length of said doctor blade and defining an elongated area ofcontact with said cylindrical surface, and means supporting said doctorblade relative to said cylindrical surface with the longitudinaldimension of said doctor blade oriented generally transversely of thedirection of rotational movement of said cylindrical member wherebyloading forces exerted upon said doctor blade are directed thereagainstin a direction substantially perpendicular to the longitudinal dimensionthereof and deflection of said doctor blade pursuant to such loadingforces is compensated for in said compressed segments by furthercompression of said segments in those portions of the abutting facesthereof disposed along the inside of the line of curvature of saidassemblage and by relief of less than all of the compression in thoseportions of said abutting faces that are disposed along the outside ofsaid line of curvature of said assemblage without physical separation ofsaid segments at their abutting faces.